As conventional focus detection apparatuses for, e.g., a camera, a re-imaging type apparatus shown in FIG. 14, and a lens array type apparatus shown in FIG. 15 are known.
More specifically, light beams 8A and 8B passing through an exit pupil 2 of a photographing lens 1 become incident on a point V on a focus detection plane 3. Thereafter, in FIG. 14, the beams become incident on points PA and PB on image sensors 6A and 6B through re-imaging lenses 5A and 5B. Therefore, as is well known, a shift between images on the image sensors 6A and 6B can be detected to determine the relationship between the focus detection plane 3 and a focal plane.
In FIG. 15, the light beams 8A and 8B become incident on light-receiving sensors a1 and b1 via a lenslet L1 arranged near the focus detection plane 3 and located at the point V. Therefore, as is well known, a shift between an image obtained by a light-receiving sensor array a1, . . . , an and an image obtained by a light-receiving sensor array b1, . . . , bn can be detected to determine the relationship between the focus detection plane 3 and a focal plane.
[Problem to be Solved by the Invention]
In either case, however, since a position (setup pupil position), on the optical axis, of a detection pupil used in focus detection is fixed at a position P0.1, a photographing lens free from an eclipse is limited. The setup pupil position is a conjugate position for a field lens 4 of the re-imaging lenses 5A and 5B in FIG. 14, or a position where a projection image from the sensors a1 to an and a projection image from the sensors b1 to bn overlap each other in FIG. 15. Since various photographing lenses, i.e., photographing lenses having exit pupils at different positions are mounted on a camera body having such a focus detection apparatus, focus detection may be disabled for the following reasons.
For example, when the setup pupil position of the exit pupil 2 of the photographing lens is the position P0.1, no eclipse occurs at a point W on the focus detection plane 3 near the optical axis of the photographing lens and even at the point V separated from the optical axis. However, when an exit pupil 21 is present at a position P0.2 separated from the setup pupil position although a full-open F number remains the same, the light beam 8B causes an eclipse at the point V separated from the optical axis, and focus detection is disabled.
This drawback becomes more conspicuous as the point V to be subjected to focus detection is separated farther from the optical axis of the photographing lens, and as the exit pupil position of the photographing lens is separated farther from the setup pupil position.
In the re-imaging type apparatus shown in FIG. 14, when an image range (V to T) detected by the re-imaging lenses is widened, a focus detection apparatus 30 becomes bulky as compared to a lens array type apparatus 40 (FIG. 15).
It is the first object of the present invention to provide a focus detection apparatus which can perform focus detection at a position separated from the optical axis of an exchangeable photographing lens in a direction perpendicular to the optical axis regardless of an exit pupil position of the photographing lens.
It is the second object of the present invention to provide a focus detection apparatus which does not require a large space as compared to a conventional re-imaging type focus detection apparatus.
Disclosure of Invention
In order to achieve the above objects, according to the present invention, a detection image range used in focus detection is limited to a small region smaller than a detection image range of a conventional re-imaging type apparatus, and the way of setting use regions on an image sensor is changed in accordance with the position of an exit pupil of a photographing lens and an aperture position (a position separated from the optical axis in a direction perpendicular to the optical axis) of a re-imaging lens, that is, a region changing means for changing the way of setting an image shift calculation region for comparing an image shift is provided, thus allowing focus detection free from an eclipse.